Conventional integrated circuits manufacturing frequently includes the formation of active devices such as transistors upon an appropriate substrate. The active devices are next covered with a dielectric material. Openings, often termed "windows" or "vias," are created in the dielectric. Next a conductive material, typically, a metal containing predominantly, for example, aluminum (and its alloys, such as those containing silicon and/or copper or both) is deposited in an argon atmosphere often by sputtering or physical wafer depostion, or tungsten by chemical wafer depostion, in a layer over the dielectric and within the opening.
An anti-reflective coating (ARC) (usually silicon) is deposited over the conductor to facilitate lithography. Then the conductor is subsequently patterned to form conductive runners between individual devices.
It is important that the anti-reflective coating thickness be maintained comparatively uniform so that spurious reflections are not created--thus interfering with subsequent lithography. It is also important that whatever conductive material is deposited, the opening be adequately filled to insure good electrical contact between the underlying device and the runner (and ultimately other devices in the circuit).
Aluminum is often used as a material for conductive runners. It has been found that the performance of aluminum runners in integrated circuits depends somewhat upon the conditions under which the aluminum runners are formed.
Various factors may affect the deposition of aluminum layers. Some of these factors are discussed below. In recent years, stress-induced voids have been reported as a major mode of failure for aluminum lines. Stress-induced voiding is due to tensile stresses generated in the aluminum lines during the cooling that follows deposition of an oxide or a nitride passivation layer. It has been found that increasing the metal deposition temperature helps to reduce problems associated with stress-induced voiding.
However, the higher deposition temperature can give rise to a new problem, namely the pull-back of deposited aluminum layers in vias and windows. The pull-back phenomenon (schematically illustrated in FIG. 1) is exacerbated as the deposition temperature is increased.
As mentioned before, after the aluminum is deposited, an ARC is formed upon the upper surface of the aluminum. The ARC is generally boron-doped amorphous silicon. Should the aluminum/ARC combination be heated, the silicon ARC tends to migrate into the aluminum. Consequently, the thickness of the ARC changes. The change in thickness of the ARC is evidenced by "rainbowing," i.e., multicolored reflections emanating from the variable thickness silicon ARC. However, maintenance of a relatively constant ARC is important to the success of the following lithography steps in achieving uniform linewidths.